Adrenergic drugs are also called sympathomimetic drugs be-cause they produce effects similar to those produced by the sym-pathetic nervous system.
Adrenergic drugs are classified into two groups based on their chemical structure—catecholamines (naturally occurring as well as synthetic) and noncatecholamines.
Adrenergic drugs are also classified by how they act. They can be:
§ direct-acting, in which the drug acts directly on the organ or tis-sue innervated (supplied with nerves or nerve impulses) by the sympathetic nervous system
§ indirect-acting, in which the drug triggers the release of a neu-rotransmitter, usually norepinephrine
§ dual-acting, in which the drug has both direct and indirect ac-tions. (See Understanding adrenergics.)
The therapeutic uses of adrenergics—catecholamines as well as noncatecholamines—depend on which receptors they stimulate and to what degree. Adrenergic drugs can affect:
§ alpha-adrenergic receptors
§ beta-adrenergic receptors
§ dopamine receptors.
Most adrenergics produce their effects by stimulating alpha recep-tors and beta receptors. These drugs mimic the action of norepi-nephrine and epinephrine.
Dopaminergic drugs act primarily on receptors in the sympathetic nervous system stimulated by dopamine.